Subcritical Reactor Research Articles

Energy Production and Transmutation of Nuclear Waste by Accelerator Driven Systems

There is a significant amount of highly radiotoxic long-life nuclear waste (NW) produced by NPP (Nuclear Power Plants). Transmutation is a process which transforms NW into less radiotoxic nuclides with a shorter period of half-life by spallation neutrons or radiative capture of neutrons produced by ADS (Accelerator Driven System). In the processes of transmutation new radioactive nuclides are produced. ADS is big energy consumer equipment. It is a method for production of a high-flux and high-energy neutron field. All these processes occur in ADS simultaneously. ADS is able to transmute actinides and produce energy simultaneously. The article considers the energy production problems in ADS. Several ideas are developed regarding the solution of the global energy supply.

Target test facility for ADS and cross-section experiment in J-PARC

For the development of Accelerator Driven System (ADS), a Transmutation Experimental Facility (TEF) is planned to be built in J-PARC. In this facility, negative hydrogen (H−) beam with a power of 250 kW will be delivered to a Lead-Bismuth Eutectic (LBE) target, which is one of the powerful candidates target for the ADS, placed at ADS Target Test Facility (TEF-T). On the beam transport to TEF-T, laser charge exchange (LCE) technique will be utilized to Transmutation Physics Experimental Facility (TEF-P) to deliver a very low-intensity beam such as 10 W with high stability from high-intensity H− beam. To examine this technique, we carried out the experiment at the RFQ test bench. By using the LCE, very stable short pulse beam extraction has been demonstrated for a long duration. We have started the development of beam monitor for the TEF-T by using heavy ion to give high DPA rate. Some experiments for validation of code and nuclear data are planned in J-PARC to obtain nuclear data for the ADS.

The measurements of neutron energy spectrum at 180 degrees with the mercury target at J-PARC

Spallation neutron production at 180 degrees is of importance for an evaluation of radiation protection for ADS (Accelerator-Driven System) and nuclear physics. It was, however, quite difficult to measure this. We measured the energy spectrum of spallation neutron at 180 degrees at the proton transport beam line (3NBT) to MLF (Materials and Life Science Experimental Facility) on J-PARC using a NE213 liquid scintillator. The irradiated proton energy was 3 GeV, and the intensity was 1 × 1010 protons. The neutron energy was determined by a Time-Of-Flight method with n-gamma discrimination. We also simulated the energy spectrum by using the PHITS code and compared this with measured spectrum. In this paper, the overview of the experiment and the results are described.

Shielding analysis of Transmutation Experimental Facility

The Japan Atomic Energy Agency is planning to construct the Transmutation Experimental Facility (TEF) to promote research, development, and demonstration of elemental technologies for accelerator-driven systems (ADSs). At ADS Target Test Facility (TEF-T), 250-kW H– beams accelerated by the 400-MeV LINAC will be derived to a lead-bismuth eutectic target. Toward the construction of TEF, a shielding analysis is carried out for the whole structure of the TEF-T in detail. The analysis for the beam tunnel shows that backward neutrons produced from the LBE target have large a impact on the radiation dose in the TEF beam tunnel. This paper presents the analytical results for components such as target station, hot cell and beam tunnel, and the shielding structure of the whole TEF.

The Experimental Investigation of Wetting Property for Liquid Lead Bismuth Alloy With ADS Materials

The accelerator-driven subcritical system (ADS) has potential economy and safety and relatively mature technology base, which has been chosen as a priority development advanced nuclear system. Liquid lead bismuth eutectic (LBE) is selected as the spallation target material and core coolant. The reduced activation ferritic/martensitic (RAFM) steel and the silicon carbide composite (SiC ${_{f}}$ ) are selected as its structural material and functional material, respectively. In the present experimental investigation, the special vacuum experimental device has been built, and the “dispensed droplet” modification of the classic sessile droplet technique has been used to investigate the wetting property and interfacial interactions for LBE/RAFM steel, LBE/316L, LBE/SiC, and LBE/SiC f couples. The contact angles were measured between the liquid LBE and the various candidate materials under working temperature from 300 °C to 480 °C. The results could provide meaningful compatibility database of liquid LBE and valuable engineering design reference of candidate structural materials and functional material for future ADS.

Coupled system thermal-hydraulic/CFD analysis of a protected loss of flow transient in the MYRRHA reactor

Within the MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) project, the Belgian Nuclear Research Centre SCK•CEN is developing and designing a flexible irradiation facility, configured as an accelerator driven system (ADS) with a MOX fueled reactor core, able to operate in both critical and sub-critical modes. The system design features a compact pool-type primary cooling system operating with molten Lead-Bismuth Eutectic (LBE). With regard to the thermal-hydraulic design and safety assessment of the installation, a major challenge is represented by the complex coolant flow field characterizing the large open regions of the primary vessel, namely the cold and hot plenum, with the presence of pronounced three-dimensional phenomena that may impact the evolution of accidental transients such as loss of flow events. In order to have a realistic representation of such effects, a coupled system thermal-hydraulic/CFD model of the MYRRHA reactor is developed and presented in this paper. The proposed multi-scale methodology, which couples the 1D system code RELAP5-3D to the CFD code FLUENT, is based on domain decomposition and a novel implicit numerical scheme is developed. The coupled reactor-scale computational model is applied in this work to the analysis of a postulated protected loss of flow (PLOF) accident, and preliminary validated against RELAP5-3D stand-alone solution data. The results of the analysis were found in agreement, demonstrating the capability of the tool to perform integral simulation taking into account 3D flows and local phenomena.

A direct calculation method for subcritical multiplication factor in Reactor Monte Carlo code RMC

The subcritical multiplication factor ks with the existence of external source neutrons is important for the evaluation of the neutron multiplication M, especially in the accelerator-driven system (ADS) performance assessment. The effective multiplication factor keff calculated from the traditional source iteration method in Monte Carlo codes can’t fully describe the subcritical system, acquiring the spurious neutron flux distribution. A direct Monte Carlo method called modified source iteration method by external source is introduced to calculate the subcritical multiplication factor ks directly, acquiring the real neutron flux at the same time. Compared with Monte Carlo fixed source calculation, the modified source iteration method has a great advantage in calculating the subcritical multiplication factor ks and its statistical error directly, especially for systems with complex geometry and a variety of fissile materials where much post-processing work on the tally results from fixed source calculation is needed. Moreover, much calculation time can be saved through this method when obtaining the subcritical multiplication factor ks with similar precision. This method has already been implemented in Reactor Monte Carlo code RMC including parallel calculation capability and can be effectively applied to the analysis of accelerator driven subcritical system (ADS).

Characterisation of multiphase ceramic coatings fabricated via laser in situ reaction technology

ABSTRACTCoatings are pre-fabricated on the China low activation martensitic (CLAM) steel via thermal spraying using Cr–Fe–Al–Ti mixed powders. Crystalline and amorphous multiphase ceramic coatings are formed by a new laser surface in situ prefabricated coatings in situ reaction technology under atmospheric environments based on the Standard Gibbs free-energy theory. The grain boundary of incomplete recrystallisation section and perfect crystallisation section can be observed clearly by high-resolution transmission electron microscopy. The Al2O3 and TiO2 are found to be formed in the crystallisation section. In addition, we adopt a new method to measure bonding strength of coating and base material, and the average shear strength is found to be 290 MPa. Further finite-element analysis shows that the shear stress distribution between the coatings and substrate is consistent with the experimental data. The average microhardness of the coatings is found to reach 1864.19 HV0.2.The coatings also exhibit the strongest liquid Pb corrosion resistance. This technique may be important in technological improvement of surfaces of the candidate structural materials for the accelerator-driven sub-critical system, which is usually applied to handle the nuclear waste under extreme conditions.

Initial thermal-hydraulic assessment by OpenFOAM and FLUENT of a subcritical irradiation facility

Aim of this work is the preliminary thermal-fluid-dynamic assessment of a subcritical system to perform integral measurements on transmutation processes, designed in the frame of EU CHANDA project: in particular, a low power Accelerator Driven System (ADS) may represent an attractive intermediate step to fill the gap between existing and future facilities like MYRRHA (or possibly EFIT). The activity finds its place within the roadmap for the evaluation of transmutation processes in ADSs, where currently measurements are performed on the zero-power ADS Guinevère at SCK·CEN (Mol, Belgium), while in the future it is expected that MYRRHA will be the major high-power facility for performing this kind of studies and assessing the performance of a fast ADS.The neutronic characterization and burn-up simulations based on MCNP6 code of the reactor core allowed the definition of the geometry and the composition of the fuel assembly and, therefore, the thermal power to be removed. On this basis a thermo-fluid-dynamic assessment, through simple analytical accounts and detailed 3D CFD calculations by OpenFOAM-v1612+ and ANSYS FLUENT v17.0 was made.The present paper is an extended version including the main conclusions and observations emerged in the 2nd AIGE-IIETA International Conference in Genoa.

Research and development activities for accelerator-driven system in JAEA

The Japan Atomic Energy Agency (JAEA) has investigated an accelerator-driven system (ADS) to transmute minor actinides which will be partitioned from the high level waste. There are various inherent issues for the research and development on the ADS. The recent two activities to realize a feasible and reliable ADS concept are introduced in this paper.For the feasibility, the design of a beam window which is a boundary of the accelerator and the subcritical core, is one of the most important issues. To mitigate the design condition of the beam window, namely to reduce the necessary proton beam current, the subcritical core concept with subcriticality adjustment rods was investigated. Through the coupled analysis of neutronics, particle transport, thermal-hydraulics and structure, a feasible beam window concept was presented.For the reliability, a beam-trip is the inherent and serious issue for the ADS design because it induces a rapid temperature change in structures in the subcritical core. In the previous study, the beam-trip frequency of the ADS accelerator was estimated based on the operation data of the existing accelerators. To minimize the beam-trip frequencies, a double-accelerator concept was proposed and its beam-trip frequency was estimated. The results indicated that the double-accelerator concept was useful to realize reliable accelerator operation for the ADS although the cost of the accelerators and those buildings would be double.

Transient safety analysis for simplified accelerator driven system with gas-lift pump

Owing to remarkable advantage for transmutation of the long-lived nuclear waste, Accelerator Driven System (ADS) is one of the most promising systems in nuclear power field. In this study, the transient analysis of a simplified lead bismuth alloy cooling accelerator driven system with gas-lift pump has been numerically simulated. By using point reactor neutron kinetics equation and related thermal-hydraulic models, TASAR (Transient Analysis of Simplified ADS Reactor) code is developed. The five kinds of transient cases are simulated: Starting gas-lift pump (SG), Unprotected loss of flow (ULOF), Beam interruption (BI), Unprotected transient over current (UTOC), Unprotected transient overpower (UTOP). Meanwhile, the calculation results of TASAR code are validated by the experimental data of NACIE (Natural Circulation Experiment) facility. The analysis is as following: In SG and ULOF conditions, the introduction of gas-lift pump has a remarkable influence of loop natural circulation capability. In BT and UTOC conditions, the short-time beam cutting off and a 100% increase of the external neutron source would not lead to the immediate fuel melting. In UTOP condition, a reactivity jump of 2$ would not lead to the damage of fuel and the cladding. The above numerical results show that, the accelerator and gas-lift pump influence the loop mass flow rate and core temperatures of research system in this paper greatly, and the simplified accelerator driven system with gas-lift pump has a very good safety performance.

Experimental investigation of gas lift pump in a lead-bismuth eutectic loop

The gas lift pump has been used in the development of an Accelerator Driven System (ADS) nuclear reactor instead of mechanical pumps due to its simple mechanical structure. The two phase flow of Lead Bismuth eutectic (LBE)-inert gas in rising pipe could remarkably increase natural circulation capacity. This study aims to evaluate the performance of the gas lift pump and to conduct the relevant parametric study. As a result, the Natural Circulation Capability Loop (NCCL) test facility was designed and constructed. The height of the experimental loop is 4.5 m and the rising height is 3.5 m. The maximum temperature of the loop is 500 °C. The experiments about the gas lift pump in LBE were performed with risers of three different heights. The results showed that the LBE mass flow rate increases rapidly with an increase of argon flow rate when it is less than 300 NL/h. When the argon flow rate is larger than 300 NL/h, the growth of the LBE mass flow rate is reduced. The LBE mass flow rate increased process is accompanied by the transformation of the flow pattern. The variation trend of the LBE flow rate is consistent with the trend of the void friction in the riser. Under the same amount of argon gas injection, the LBE circulation ability increases as the height of the riser increased. Based on the experimental data and drift-flow model of Zuber and Findlay, a new correlation of the void fraction is obtained and the relative error between the calculated and the experimental value is within 30%. The purpose of this study is to reveal the enhancement mechanism of the natural circulation capacity of gas lift pump and to provide experimental data and model support for the design of ADS in China.

Simulation and test of Fuel Handling System for Accelerator Driven Subcritical Reactor

For the fuel handling in Accelerator Driven Subcritical Reactor (ADSR), some key issues should be considered, such as the accelerator proton beam tube blocking, the liquid metal corrosion and the radiation. As a critical part of the reactor, the innovation design of the double rotating plugs and split-type center column scheme of the Fuel Handling System in the vessel was proposed according to the features of ADSR. A location computation model for the computer simulation was established based on the system. Through the comparative analysis between the numerical simulation results, the proposed structure is optimized and the operating range of the system can completely cover the refueling operation range of the core. Then, a principle prototype in air condition has been developed and tested. The simulated automatic refueling that covering all assemblies was realized on the prototype.

Np-237 incineration study in various beams in ADS setup QUINTA

Abstract Neptunium-237 samples were irradiated in a spallation neutron field produced in accelerator-driven system (ADS) setup QUINTA. Five experiments were carried out on the accelerators at the JINR in Dubna - one in carbon (C6+), three in deuteron, and one in a proton beam. The energy in carbon was 24 GeV, in deuteron 2, 4 and 8 GeV, respectively, and 660 MeV in the proton beam. The incineration study method was based on gamma-ray spectrometry. During the analysis of the spectra several fission products and one actinide were identified. Fission product activities yielded the number of fissions. The actinide (Np-238), a result of neutron capture by Np-237, yielded the number of captures. The main goal of this work was to find out if and how the incineration rate depended on parameters of the accelerator beam.

Conceptual design study of beam window for accelerator-driven system with subcriticality adjustment rod

The design of the beam window of the spallation target is one of the critical issues in the accelerator-driven system (ADS) design. This study aims to perform the coupled analysis for the feasible beam window concept. To mitigate the design condition, namely to reduce the necessary proton beam current, subcriticality adjustment rod (SAR) was installed to the ADS core. The burnup analysis was performed for the ADS core with SAR and the results indicated that the maximum proton beam current during the burnup cycle was reduced from 20 to 13.5 mA.Based on the burnup analysis result, the coupled analysis; particle transport, thermal hydraulics and structural analyses, was performed. As the final result, the most robust beam window design; the hemisphere shape, the outer radius = 235 mm, the thickness at the top of the beam window = 3.5 mm and the factor of safety for the buckling = 9.0, was presented. The buckling pressure was 2.2 times larger than the previous one and more feasible beam window concept was presented through this study.

The research on the characteristics of target and core in a gas-cooled ADS with passive safety

The Accelerator Driven Subcritical Reactor System (ADS) has a strong ability to transmute minor actinides (MAs) and it has inherent safety because of its subcritical core. However, the removal of decay heat is a major problem for the ADS and the design of spallation target is still a difficulty. Therefore, this paper presents a design of gas-cooled ADS with passive safety to attain the good performance of removing decay heat and transmutation.For the design of the target, the helium-cooled tungsten target is decided to adopt, and it is modelled into the cone structure to strengthen the convective heat transfer. A series of numerical experiments have been made to determine the optimal parameters of the target using the MCNP and CFX code. In the design of core, the subcritical core is divided into fast neutron region which the MAO2 is placed in and thermal neutron region which the UO2 is placed in to improve the performance of the transmutation. Two methods are proposed in this paper for the thermal-hydraulic calculation in the steady-state analysis, and the results show its good thermal performance.

Numerical analysis of the granular flow and heat transfer in the ADS granular spallation target

The Accelerator-Driven System (ADS) is one of the most effective tools to deal with the spent fuels by nuclear transmutation. In the ADS, the neutrons could be produced by bombarding a proper spallation target with a concentrated beam of high-energy accelerator protons. Subsequently, the produced neutrons drive the nuclear transmutation in the sub-critical reactor. Therefore, the spallation target is an essential part of the ADS. Recently researchers proposed a gravity-driven dense granular target, which has both solid and fluid target characteristics.This study developed the FOCUS code to simulate the granular flow and heat transfer behaviors involved in the gravity-driven dense granular target. A solid sedimentation experiment was performed and simulated by FOCUS code. The simulation results were consistent with the findings in the experiment, which proved FOCUS to be an appropriate code to simulate the granular flow. Then the sensitivity analyses were performed to investigate the influence of the inlet flow rate and the target area shape on the state of the granular flow in the ADS granular spallation target. The simulation results showed that the velocity of each granular spallation target was related with the height of piled-up particles in the targets area. The geometry size of the target area obviously affected the flow state of targets. Meanwhile the inlet flow rate had a slight influence on the stable flow, unless the inlet flow was so large that targets overflow the target area. Furthermore, the study also calculated the heat transfer between each target and found that heat conduction between two contacted granular spallation targets was the main process in the targets area. The present work would be instructive for the ADS system design.

Investigation of Novel Composite Material Based on Extra-Heavy Concrete and Basalt Fiber for Gamma Radiation Protection Properties

The paper presents a new composite material for radiation protection based on extra-heavy concrete reinforced by basalt fiber. Basalt fiber is a new material for concrete reinforcement, which provides improved mechanical characteristics of concrete, reduces the level of microcracks and increases the durability of concrete. Within the scope of present work, the gamma-ray radiation protection properties of concrete reinforced with basalt fiber was modeled. Two types of extra-heavy concrete were used for this paper. The main gamma-ray attenuation coefficients such as mean atomic number, mean atomic mass, mean electron density, effective atomic number, effective electron density, Murty effective atomic number were analyzed with help of WinXCom software. It has been shown that the addition of basalt fiber to concrete does not impair its gamma-ray radiation shielding properties. With increasing the basalt fiber dosage in concrete, the radiation properties against gamma radiation are improved.
 This research was carried out with the financial support of the IAEA, within the terms and conditions of the Research Contract 20638 in the framework of the Coordinated Research Project (CRP) “Accelerator Driven Systems (ADS) Applications and use of Low-Enriched Uranium in ADS (T33002)” within the project “The Two-Zone Subcritical Systems with Fast and Thermal Neutron Spectra for Transmutation of Minor Actinides and Long-Lived Fission Products”.

Uncertainty quantification of criticality in solid-moderated and -reflected cores at Kyoto University Critical Assembly

ABSTRACT Uncertainty quantification is conducted for the criticality of excess reactivity and control rod worth obtained at the Kyoto University Critical Assembly (KUCA). By combining SRAC2006 and MARBLE code systems, the sensitivity coefficients of the cross sections for aluminum-27 (27Al) comprising mainly of core components are large in the solid-moderated and -reflected cores (A cores) at KUCA. Also, the uncertainty is dominant in the uranium-235 isotope by the covariance data of JENDL-4.0, and a quantitative value is about 150 pcm induced by the JENDL-4.0 data library in the KUCA A cores, whereas the covariance data of 27Al are not prepared in JENDL-4.0. Moreover, the effect of decreasing uncertainty is obtained by applying the cross-sectional adjustment method to the uncertainty analyses. From the results, a series of uncertainty quantifications is expected to clarify the uncertainty of sub-criticality in accelerator-driven system experiments with spallation neutrons in the KUCA A cores.

Preliminary analysis of reactivity reconstruction capability based on inverse kinetics method under different initial reactivity states

Online reactivity monitoring plays an important role in operation and safety analyses of fission reactor systems. The inverse kinetics method, which is based on a point kinetics model, is the most widely used method for reactivity reconstruction of critical water reactors. However, this method is seldom applied to the reactivity reconstruction of subcritical reactors. In this study, an inverse kinetics method was employed for the reactivity reconstruction of a lead-based reactor under different initial reactivity states (ρ0 = 0, − 2786, − 5486, − 8367, and − 12,371 pcm). The results showed that the deviation in the reactivity of the lead-based subcritical reactor was greater when ρ0 became smaller. The reactivity reconstructed using the inverse kinetics method was globally underestimated. At a given reactivity perturbation, the relative and absolute errors increased with the decrease in the initial reactivity. At a given initial reactivity, with the increase in the reactivity perturbation, the absolute error increased, whereas the relative error remained the same. This deviation is due to the variation in the external neutron source, spatial-spectral effects, and sub-diffusive effects, which require further study.